/* Using kill for Communication

   Copyright (C) 1991-2018 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or

   modify it under the terms of the GNU General Public License

   as published by the Free Software Foundation; either version 2

   of the License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with this program; if not, if not, see <http://www.gnu.org/licenses/>.

*/

/*@group*/

#include <signal.h>

#include <stdio.h>

#include <sys/types.h>

#include <unistd.h>

/*@end group*/

/* When a @code{SIGUSR1} signal arrives, set this variable.  */

volatile sig_atomic_t usr_interrupt = 0;

void

synch_signal (int sig)

{

  usr_interrupt = 1;

}

/* The child process executes this function. */

void

child_function (void)

{

  /* Perform initialization. */

  printf ("I'm here!!!  My pid is %d.\n", (int) getpid ());

  /* Let parent know you're done. */

  kill (getppid (), SIGUSR1);

  /* Continue with execution. */

  puts ("Bye, now....");

  exit (0);

}

int

main (void)

{

  struct sigaction usr_action;

  sigset_t block_mask;

  pid_t child_id;

  /* Establish the signal handler. */

  sigfillset (&block_mask);

  usr_action.sa_handler = synch_signal;

  usr_action.sa_mask = block_mask;

  usr_action.sa_flags = 0;

  sigaction (SIGUSR1, &usr_action, NULL);

  /* Create the child process. */

  child_id = fork ();

  if (child_id == 0)

    child_function ();		/* Does not return.  */

/*@group*/

  /* Busy wait for the child to send a signal. */

  while (!usr_interrupt)

    ;

/*@end group*/

  /* Now continue execution. */

  puts ("That's all, folks!");

  return 0;

}